Water is often called the “universal solvent” because it can dissolve more substances than any other liquid. A solvent is a substance that dissolves other substances, called solutes, to form a solution. This property is fundamental to many natural processes and daily life applications, stemming from its unique molecular characteristics.
Water’s Unique Molecular Structure
A single water molecule (H₂O) consists of one oxygen atom bonded to two hydrogen atoms. The oxygen atom is more “electron-greedy,” a property called electronegativity, pulling shared electrons closer. This unequal sharing causes the oxygen atom to develop a slight negative charge, while the hydrogen atoms develop slight positive charges. This separation of charges makes water a polar molecule, similar to a tiny magnet.
The water molecule has a bent shape because the oxygen atom has two unshared pairs of electrons that repel the bonding pairs. This bent geometry ensures the partial charges do not cancel out, reinforcing the molecule’s overall polarity. Due to this polarity, water molecules are attracted to each other, forming hydrogen bonds. These bonds are weaker than covalent bonds but collectively contribute to water’s unique properties.
How Water Dissolves Substances
Water’s polarity allows it to effectively dissolve many substances. When an ionic compound, like table salt (sodium chloride), is added to water, water molecules are attracted to the charged ions. The slightly negative oxygen ends surround positive ions, while the slightly positive hydrogen ends surround negative ions. This attraction pulls ions away from their solid crystal lattice, breaking their bonds. Water molecules then form a “hydration shell” around each ion, preventing them from rejoining and keeping them dissolved.
Water also dissolves polar covalent compounds, such as sugar, through hydrogen bonding. These compounds have regions of partial positive and negative charges. Water molecules form new hydrogen bonds with the polar regions of the solute molecules, surrounding and separating them. This process allows the solute molecules to disperse evenly throughout the water.
Non-polar substances, such as oils and fats, do not dissolve in water because they lack the partial charges water can interact with. Water molecules are more attracted to each other through hydrogen bonds than to non-polar molecules. When a non-polar substance is introduced, water molecules exclude it, clumping together to maintain their strong hydrogen bonding network.
The Importance of Water as a Solvent
Water’s solvent properties are important to life and countless processes. In biological systems, water acts as the medium for transporting nutrients, waste products, and gases throughout living organisms. For example, blood plasma, over 90% water, dissolves and carries substances like glucose, hormones, and electrolytes to cells, while also removing waste. Many biochemical reactions within cells also occur in water, as it allows dissolved chemicals to move and interact.
Beyond biology, water’s dissolving power is widely utilized in everyday life and industrial applications. It is used for cleaning, as it can dissolve and carry away dirt and grime. In cooking, water dissolves flavors and helps change the consistency of food. Industrially, water is used as a solvent in the production of a vast array of products, including medicines, fertilizers, paints, and paper. Its ability to dissolve various substances makes it a key component in many manufacturing and processing operations.